Examples of such type of human body detecting device include an infrared human body detector that includes a pyroelectric element and an optical system disposed ahead of the photosensitive surface of the pyroelectric element (refer to patent literature 1).
A pyroelectric element includes multiple elements (detecting unit) having output voltage polarities different from each other. The optical system includes a mirror and a lens body (a lens array). The lens body includes multiple lenses.
In the above-described infrared human body detector, output of the pyroelectric element is amplified by the amplification unit, the output is passed through a bandpass filter, and then determination is made by the comparator circuit whether or not the output level is higher than a reference level. This allows the infrared human body detector to detect the existence and/or motion of a person.
A human body detecting device sometimes cannot detect the motion of a person when they move from the outside of a detection area into the detection area, and thus increasing the sensitivity has been requested.